If you are running Firepower Management Center you can create custom reports under Overview>Reporting>Report Templates.
I looked a bit more into this and I don't think you can create a report on top URLs / Websites.
You can create a report for top URL Categories in release 6.2.2.
I have tried to make something that hopefully looks like what you are looking for.
I have made it so you also get a dashboard to look at.
1. Go to Analysis - Custom - Custom Tables
2. Create Custom Table
3. Name it, In Tables choose Connection Events and in field URL and add that.
4. In Tables choose Hosts and IP Address and add that.
5. Tick in Initiator IP
6. Now its back in Custom Tables window, now click Magnifying class next to your new Custom Table
7. That will get you to table view. There you edit search so can search for what you want.
8. Edit Search and write what you need. (see my screenshot for what i got), Whatever IP range you need. In url i have entered http://www. and https://www. that removed all the analytics links. I think with the http and https in url gives me a better view of websites. Then save your search.
9. Then you go to dashboard and add a Custom Analysis. In table you pick the name of the table you created. In field you pick url and in search you pick the name of the search you just created.
10. Then you get your dashboard view and you can click on report designer in top, to make a report from that.
See all attached screenshots.
Hope i covered it all. Otherwise just ask :)